You have gone on holiday to Kenya to watch wild animals - a safari holiday. On the morning of the first trip to see some animals, the tour guide hands you a piece of paper with suggestions of things to take with you for the day. He suggests that you take a hat, some mosquito repellent and a long-sleeved shirt. He also suggests that you wear comfortable shoes. He also suggests that you take your camera.
When he wrote the last sentence, he realised that some people might have forgotten to pack their camera when they left home to fly to Kenya. So he adds "unless you haven't brought it", meaning "unless you have not brought your camera from your home country to Kenya". Obviously, if you haven't brought your camera to Kenya, you can't take your camera with you on safari for the day. Consequently, the phrase "Take your camera unless you haven't brought it" is possible!